This invention relates to a bearing comprising a fixed element and a concentric moving element, and preferably comprises concentric inner and outer races having a plurality of rolling elements therebetween.
WO-A-2010/035011 discloses a bearing for a wind turbine in which the race which is normally fixed with respect to ground is adapted to idle in a controlled manner. Such an arrangement allows the static load to be supported around the entire circumference of the normally fixed race, rather than being taken continuously by the same upward facing portion. As a result bearing life can be substantially enhanced. Various means and methods of generating controlled idle rotation are disclosed. Idle rotation should be sufficiently slow to avoid wear of the bearing, but fast enough to avoid damage caused by sustained static loads.